Phenol-formaldehyde (PF) resins, as well as PF resins extended with urea (PFU resins), have been the mainstays of fiberglass insulation binder technology over the past several years. Such resins are inexpensive and provide the cured fiberglass insulation product with excellent physical properties.
One of the drawbacks of this technology, however, is the potential for formaldehyde emissions during the preparation of the adhesive resin, during the manufacturing of the fiberglass insulation and during its subsequent use.
Fiberglass insulation is typically made by spraying a dilute aqueous solution of the PF or PFU resin adhesive binder onto glass fibers, generally hot from being recently formed, forming a mat or blanket of the binder-treated fibers and then heating the mat or blanket to an elevated temperature in an oven to cure fully the adhesive resin.
Manufacturing facilities using PF and PFU resins as the main adhesive binder component for insulation products recently have had to invest in pollution abatement equipment to minimize the possible exposure of workers to formaldehyde emissions and to meet Maximum Achievable Control Technology (MACT) requirement Standards.
As an alternative to PF and PFU resins, certain formaldehyde free formulations have been developed for use as an adhesive binder for making fiberglass insulation products. One of the challenges to developing suitable alternatives, however, is to identify formulations that have physical properties (viscosity, dilutability, etc.) and other characteristics similar to the standard PF and PFU resins, i.e., formulations which also have a similar cure time/cure temperature profile, while yielding a cured fiberglass insulation product with equivalent physical properties.
U.S. Pat. No. 5,030,507 describes an emulsion copolymer binder for nonwoven products that is alleged to cure formaldehyde free. The copolymer is prepared by the emulsion polymerization of an (meth)acrylic acid ester, in combination with styrene, acrylonitrile or vinyl acetate, and both a hydroxy(meth)acrylate and an isocyanate.
U.S. Pat. Nos. 5,198,492 and 5,278,222 describe a latex binder for cellulose, said to be especially useful where low formaldehyde emissions are important. The binder is a combination of a non-formaldehyde emitting latex admixed with an aqueous copolymer dispersion of a highly functionalized emulsion copolymer. The functionalized emulsion copolymer is a low solids emulsion, i.e., 10 to 16% by weight of solids, made from 10 to 60% of an olefinically unsaturated non-ionic organic compound and equal parts of a carboxylic acid and an olefinically unsaturated carboxylic acid hydroxy ester, or an olefinically unsaturated amide, or a mixture thereof.
U.S. Pat. No. 5,318,990 describes a formaldehyde free formulation for fiberglass insulation based on an aqueous solution of a polymeric carboxylic acid, especially a polyacrylic acid, and a monomeric triol, such as glycerol, trimethylolpropane and the like. Other polyols may optionally be present. The formulation requires the presence of a phosphorus accelerator (catalyst) in the aqueous solution to obtain an effective cure at suitable temperatures.
U.S. Pat. No. 5,340,868 describes a binder for making a fiberglass mat comprising an aqueous solution of a polymeric carboxylic acid, such as polyacrylic acid, a β-hydroxyalkylamide and an at least tri-functional monomeric carboxylic acid, such as citric acid, trimellitic acid, hemimellitic acid, trimesic acid, tricarballylic acid, 1,2,3,4-butanetetracarboxylic acid (BTCA) and pyromellitic acid.
U.S. Pat. No. 5,354,803 describes a graft copolymer of a low molecular polyvinyl alcohol (PVOH) as a formaldehyde-free binder, having a vinyl or acrylic monomer grafted onto the PVOH through emulsion polymerization in the presence of free-radical generators. Suitable monomers include acrylic acid and maleic acid.
U.S. Pat. No. 5,393,849 describes a curable composition useful in making binder formulations made by combining an unsaturated polyester resin and a polyamino compound.
U.S. Pat. No. 5,498,658 (and the related divisional U.S. Pat. No. 5,520,997) describes a self-curing, formaldehyde-free interpolymer latex binder. The interpolymer is prepared principally by emulsion polymerization from the following monomers (1) an unsaturated monomer having a nucleophile group, (2) an unsaturated dicarboxylic acid, (3) (meth)acrylonitrile and optionally (4) a (meth)acrylic acid ester and (5) styrene. As described, the unsaturated monomer having a nucleophile group has a functional group, such as an amino or hydroxyl, which in combination with the dicarboxylic acid, allows the polymer to self-cross-link. Examples of such monomers are acrylamide and hydroxypropyl acrylate (see Examples 1, 2 and 3). Representative dicarboxylic acids include maleic acid and itaconic acid.
U.S. Pat. No. 5,661,213 (and the related patents U.S. Pat. Nos. 5,763,524; 6,136,916 and 6,221,973) describes a formaldehyde free formulation for fiberglass insulation based on an aqueous solution of a polyacid, such as a polyacrylic acid, and a polyol (at least a diol), with a molecular weight less than about 1000, such as, for example, ethylene glycol, glycerol, pentaerythritol, trimethylol propane, sorbitol, sucrose, glucose, resorcinol, catechol, pyrogallol, glycollated ureas, 1,4-cyclohexane diol, diethanolamine, triethanolamine, and certain reactive polyols such as, for example, β-hydroxyalkylamides. The carboxyl groups of the polyacid are neutralized to an extent of less than about 35% with a fixed base. The formulation generally requires the presence of a phosphorus accelerator (catalyst) in the aqueous solution to obtain an effective cure at suitable temperatures.
U.S. Pat. No. 5,932,689 describes a formaldehyde free formulation for fiberglass insulation based on a combination of three components (1) a polyacid, such as polyacrylic acid, (2) an active hydrogen-containing compound, such as a polyol, or a polyamine, and (3) a cyanamide, a dicyanamide or a cyanoguanidine. In this formulation, an accelerator (catalyst) is said to be optional. Suitable accelerators include a phosphorus or fluoroborate compound. As above, the carboxyl groups of the polyacid are neutralized to an extent of less than about 35% with a fixed base.
U.S. Pat. No. 5,977,232 describes a formaldehyde free formulation for fiberglass insulation based on a combination of three essential components (1) a polyacid, such as polyacrylic acid, (2) an active hydrogen-containing compound, such as a polyol, or a polyamine, and (3) a fluoroborate accelerator.
U.S. Pat. No. 6,071,994 describes a formaldehyde-free aqueous binder comprising (1) a free-radically polymerized polymer containing from 5 to 100% by weight of units derived either from an ethylenically unsaturated acid anhydride, or from an ethylenically unsaturated dicarboxylic acid whose carboxyl groups can form an anhydride group, and (2) an alkanolamine having at least two hydroxyl groups. Based on the specific examples in this patent, polymers containing acrylic acid are preferred and all of the examples were formulated to cure at a pH of below 4.0.
U.S. Pat. No. 6,114,464 describes a binder for producing shaped articles, such as chipboard, comprising a curable composition of an addition polymer of an unsaturated mono- or dicarboxylic acid and a multi-hydroxyalkylated polyamine.
U.S. Pat. No. 6,171,654 describes preparing fiberglass insulation using a water soluble or water-dispersible curable polyester resin binder formed by reacting a polyol, such as pentaerythritol, a terephthalate polymer, such as recycled polyethylene terephthalate (PET), a polyacid, such as isophthalic and terephthalic acid, an end (mono-functional) acid, a reactive diluent (crosslinker) such as a melamine resin, and an acid catalyst.
U.S. Pat. No. 6,331,350 describes a binder formulation for fiberglass very similar to U.S. Pat. No. 5,661,213 except that the polyacid must have a low molecular weight and the pH of the aqueous solution must be adjusted to less than 3.5.
U.S. Pat. No. 6,426,121 describes dual cross-linkable emulsion polymers for use with nonwoven materials. The polymers “incorporate at least two different but reactive functionalities, i.e., hydroxy and carboxy.” The polymer is formed by polymerizing ethylenically unsaturated carboxylic acids in the presence of PVOH. Hydroxyl functionality can be incorporated using hydroxy functional acrylates. The patent does not describe the polymer as self-cross-linking and suggests cross-linking by using a dual crosslinker system of a polyaldehyde and a polyaziridine.
U.S. Publications 2004/0033747; 2004/0082240 and 2004/0082241 describe aqueous binder compositions employing a copolymer having both hydroxyl and carboxyl functions that can be used to prepare non-woven mats, such as fiberglass insulation.
Despite these disclosures, there is a continuing need for identifying new formaldehyde-free, curable aqueous compositions suitable for use as a binder, specifically for fiberglass and especially for making glass fiber products such as fiberglass insulation.
Indeed, because most, if not all, of the prior art binder formulations employing polyacid-type polymer ingredients, such as a polyacrylic acid, are formulated at an acidic pH, a pH of below about 4.0 being typical, there is a heightened risk of incurring accelerated corrosion of process equipment associated with the storage, transport, and application of the binder compositions.